Mississippi State University
Date of Degree
Dissertation - Campus Access Only
Doctor of Philosophy (Ph.D)
James Worth Bagley College of Engineering
Dave C. Swalm School of Chemical Engineering
The blending or mixing is extensively utilized in diverse processes of polymers to bring about advantageous properties, but the behavior becomes intriguing when associations are involved and multi-solvents are used. Explanations based on chemistry-specific arguments are less than satisfactory in abstracting essential features, and lack the general applicability across various systems. So, this work focuses on capturing the physical force governing the phenomenon of interest by using a generic model. Highly non-trivial behaviors of polymers are often observed in multi-solvent solutions. It is known that polymers swell and dissolve in good solvents, while they tend to collapse and aggregate in poor solvents. But for some specific systems, polymers that collapse in two different poor solvents become soluble in their mixtures, corresponding to cosolvency, and conversely, polymers that swell in two different good solvents become insoluble in their mixtures, pertaining to cononsolvency. The finding suggests that cononsolvency effect relies on the interplay between polymer-cosolvent preferential adsorptions and solvent-cosolvent attractions, which are typically investigated individually. The utilization of cononsolvency effect can either modify or induce micellization, leading to significant differences in morphology and thermodynamic properties compared to conventional micelles driven solely by hydrophobic interactions. The cosolvency project reveals that it arises from the cross competitions of Van der Waals-type interactions and the associative interaction (e.g., hydrogen bonding). The molecular association has long been a classical problem in physical chemistry, as it often gives rise to ”abnormal” phenomena, such as the elevation of boiling points due to hydrogen bonding. But the understanding of its effect on polymer system still remains rudimentary. So, this work tries to answer three fundamental questions by choosing three representative systems: 1. How will supramolecular complexations change the thermodynamics equilibrium morphology; 2. What is the impact of supramolecular bonds on the free energy landscape during the transition process; 3. How will association influence the single chain coil-globule conformational transition. It is found that the association not only results in versatile morphology, but also brings about distinct transition pathways. Besides, the conformational transition shows the dependence on the association pattern, which is actually decided by the statistical nature.
Zhang, Xiangyu, "The cosolvent and association effect on polymer behaviors" (2023). Theses and Dissertations. 5911.